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Physiology > Week 7: Microcirculation > Flashcards

Week 7: Microcirculation Flashcards

1
Q

What is the purpose of micro circulation?

A

to ensure eqilibirum with the external and internal environments

it is part of the alimentary system

examples: pulmonary, gastrointestinal, renal, and bodily microcirculation

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2
Q

Macro- micro transition:

How are the arteries and veins connected?

A

Arterial branches → arterioles → capillaries → venules → venous branches

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3
Q

What is the graph representing optimal parameter profiles

A
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4
Q

Branching

A

book

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5
Q

Coupling with the microflow environment

A

book

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6
Q

What is the microcirculatroy unit?

A

The unit that connects the arterioles and the venules

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7
Q

What is the input and output of the microcirculatory unit?

A

input: arteriole

output: venule

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8
Q

What is the “throughfare channel” and what does it allow?

A

a channel which allows blood to flow freely between an arteriole and venule

can carry nutritive flow → metarteriole, capillary network

can carry nonnutritive flow → shunt

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9
Q

What is the direction of flow in the microcirculatory unit?

A

arteriole → venule

(within the capillary, the spatio-temporal pattern is more complex)

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10
Q

What offers a means of overall control of flow?

A

the smooth muscle layer in the wall of the arteriole

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11
Q

What offers the means of local control?

A

precapillary sphincters

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12
Q

Graph displaying the different vessels v.s. pressure

A
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13
Q

The pressure is autoregulated (graph)

A
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14
Q

How is the diameter of the vessels adjusted?

A

vasomotion

the oscillation of vascular tone (diameter) with frequencies in the range from 1-20 min and is seen in the most vascular beds

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15
Q

Where does the oscillation of vasomotion originate?

A

vessel wall

(seen in vivo & vitro)

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16
Q

What must be present in order for vasomotion to occur?

A

cellular oscillator

can be modeled as a strong of events forming a feedback loop

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17
Q

In order to get macroscopic oscillations of blood vessels ____

A

the oscillations in individual smooth muscle cells must be synchronized

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18
Q

What are the physiological roles of vasomotion?

A
  1. improve flow in the periphery of circulation
    • ​​flow is better through an oscillating diameter rather than a steady one
  2. make peripheral flow distribution more efficient
    • ​​by ↑ the synchronization
  3. ↑ the reactivity of a blood vessel
    • ​​avoiding the “latch state” (state of prolonged force in SM due to low ATP)
  4. pattern alters in disease
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19
Q

Describe the flow of RBC and plasma.

A
  • flow in two phases in arteries and arterioles
  • in the capillaries their flow behavior separates int plug and bolus flows (i.e. single file
  • the plasma bolus is being stirred while flowing which provokes gas and meterial exchange betwen capillary lumen and wall
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20
Q

Why can a RBC of 7 micra in diameter fit into a capillary of smaller diameter (5 micra) ?

A

special shape and remarkable membrane flexibility

21
Q

Describe the flow of white blood cells.

A
  • flow is much slower than that of RBC
  • tend to interfere with microcirculatory flow
    • therefore WBC have impact of microcirculatory flow
22
Q

What is the impact of glycocalyx on flow?

A
  • the bushlike extracellular matrix structure penetrates the plasma column, capturing its edge
    • acts as a stagnant cell-free plasma layer
  • size of this layer effects microcirculatory hematocrit
  • molecular composition is complex and assists in multiple homeostatic functions
23
Q

What is responsible for the formation of ESL (endothelial surface layer) ?

A

interaction between soluble plasma components and the membrane-bound glycocalyx

24
Q

Discuss the ESL in regards to thickness

A

ESL thicker than glycocalyx

  • thickness of ESL ↑ with vessel diameter
  • relative thickness vise versa
  • therefore the ESL is able to withstand the sheer stress of flowing blood and exclude RBC
25
Q

What are the effects of ESL on hemodynamic parameters in the microcirculation?

A

effects the flow resistance and hematocrit because of the presence of cell-free layer and thickness

26
Q

What is the result of the loss of dynamics?

A

↓ phase separation in the macro-micro transition dimension of the circulation

27
Q

What is the result of the slower dynamics?

A
  • lesser slipping over the ESL
  • results in ↑ cellular interaction
  • results in ↑ microcirculatory viscosity

the combination of loss of dynamics and slow dynamics results in the verge of collapse

28
Q

What are capillary types defined by?

A

their endothelial lining

29
Q

Name examples of continuous capillary type

A

tight: brain

retina

intercellular clefts: skeletal muscle

myocardium

smooth muscle

skin

30
Q

Name examples of fenestrated capillary type

A

GI mucosa

glands

certain renal vessels

31
Q

Name examples of discontinuous capillary type

A

liver

bone marrow

adrenal cortex

spleen

32
Q

Different ways of passive endothelium transcapillary exchange

A
33
Q

Describe transcellular exchange

A
  • mechanism: difussion
  • what does it transport? → gases (O2, CO2, Xe)

→ lipid soluble molecules

→ water via aquaporin-1 channel

  • depends on diffusion properties of the surrounding tissues
34
Q

Describe paracellular (small pore pathway) exchange

A
  • mechanism: diffusion
  • what does it transport? → water soluble (lipophobic) molecules

→ small polar molecules ( < albumin-size)

  • via small water-filled pathways (pores): → intercullular clefts

→ interendothelial junction complex

→ gaps

→ fenestrae

35
Q

What version do we use of Fick’s Law of diffusion?

A
36
Q

What is flow limited transport?

A
  • for small molecules
  • there is rapid equilibrium between the plasma and the tissue
  • only blood flow determines how much molecule can be delivered to the tissue per unit time
37
Q

What is diffusion limited transport?

A
  • when diffusion becomes restricted and there is no equilibrium between the plasma and the tissue
38
Q

What are the complicating factors of diffusion?

A
  • attractions between molecules of solute and solvent
  • surface charge
  • pore structure
  • glycocalyx
39
Q

What is the paracellular (large pore pathway) exchange

A

mechanism: (very slow) diffusion

what does it transport? protein sized molecules

via: large waterfilled pathways (large pores)

→ large clefts

→ gaps

→ fenestrae

40
Q

What is transcytosis?

A

mechanism: vesicular transport NOT diffusion

  • translocation of macromolecules
  • flux is NOT governed by Fick’s Law
41
Q

What are the exchange pathways, mechanism, and structures of the exchange of fluid

A

exchange pathways: transcellular, paracellular

mechanism: transcellular = diffusion

paracellular = convection

structure: transcellular = AQP1 channels

paracellular = clefts, fenestrae, gap junctions

42
Q

Fluid exchange

A

book

43
Q

What are the homeostatic functions of the endothelium?

A
  • regulates adhesion, rolling, and migration of leukocytes tho the endothelium
  • maintains vessel lining that prevents formation of blood clots (thrombi)
  • supresses the proliferation of VSM
  • regulates VSM tone
44
Q

What are 2 examples of vasoactive molecules produced by endothelium?

A
  1. Prostacyclin
  2. Nitric Oxide
45
Q

Name some properties of Prostacyclin

A
  • released in response to shear stress
  • formed from arachidonic acid (AA) by the actions of cyclooxygenase (CycOx) and protacyclin synthase (PGl2Syn)

Function:

  • prevent platelet aggregation
  • prevent platelet adhesion to endothelium
  • relaxes adjacent smooth muscle via ↑ cAMP
46
Q

Name some properties of Nitric Oxide

A
  • released in response to shear stress
  • can also be stimulated by Ach
  • stimulated endothelium releases NO

Function:

  • ↑ cGMP level which produces relaxation of VSM by ↓ [Ca++] sensitivty of the myofilament
47
Q

Draw the individual and net pressures in the capillary and in the interstitium

A
48
Q

What is the equation for capillary colloid osmotic pressure? List common reflection coefficients

A
49
Q

Draw the diagram representing the factors responsible for filtration and absorption across the capillary wall

A

Physiology (28 decks)

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